1. Field of the Invention
The invention relates to a mechanism that controls zooming of a zoom lens of digital still camera (hereinafter referred to as DSC) receiving electronic signals (pulses) from MCU, in which the programmed zooming data of the zoom lens is written, and also relates to a mechanism that enables a DSC to be very compact in total size by moving a part of zoom lens elements outward from the light path of the zoom lens to make a space into which the top group of lenses can be folded and retracted inward
2. Background Art
In digital still cameras with a zoom lens, usually the zoom lens has a zooming mechanism controlled by conventional cylindrical grooved cams or a zooming mechanism operated by stepping motors being directly controlled by MCU of the DSC in which all the zooming data are programmed and installed.
The zoom lenses have a plurality of lens groups for zooming. From wide angle to telephoto, the lens groups must move correspondingly with each other. From one focal length position to another focal length position, the moving strokes of the lens groups are determined by the optical design of the lens. Usually the moving strokes of those lens groups are controlled mechanically by cylindrical grooved cams.
To enable the two groups of lenses to carry out the corresponding movements effectively, a mechanism with grooved cams is conventionally used. FIGS. 1 and 1-a show the conventional mechanical controlling system of zoom lens, which has six grooved cams. One group of lenses is controlled by one set of three grooved cams of the same curve and dimensions provided on the periphery of the outermost lens barrel (a tube to hold the whole lens assembly), and the other set of three grooved cams of the same curve and dimensions provided on the same periphery of the lens barrel controls the other group of lenses.
The first set of grooved cams (1) controls the second group of lenses (2) and the second set of grooved cams (5) controls the third group of lenses (3). At the bottom rim of the outermost lens barrel (4), the gear teeth (6) are provided and engaged with the driving gears (7) of the stepping motor (8). When the zooming switch is turned on, the stepping motor (8) starts rotating, and then the outermost lens barrel (4) starts rotating. While the outermost lens barrel (4) rotates, the grooved cams (1 & 5) move too, and the two groups of lenses (2 & 3) also move back and forth (up and down) through the movements of the cam followers (pins) (9) fixed on the lens barrel of each group of lenses and inserted into the slots of the grooved cams, which move according to the curves of the grooved cams (1 & 5). The curves of the grooved cams (1 & 5) are designed accurately according to the zooming data of the zoom lens. The direction of lens movement (back or forth) is determined by the direction of the rotation of the stepping motor.
In this kind of mechanical controlling of zooming, the accuracy of the grooved cams is highly required and it is very difficult to manufacture lens barrels with such accurate grooved cams, and consequently the cost of such accurate parts and components is quite expensive. The assembling and adjustment of the lens with such controlling mechanism are also quite difficult.
To solve the problems that the conventional cylindrical grooved cam zooming system has, an improved control system of zoom lens for DSCs has been disclosed in U.S. Pat. No. 6,453,123 issued to Arc Design, Inc., the same assignee of the subject application.
In FIG. 2, the control system of zoom lens for DSCs comprises a first (front) group of lenses (10) fixed at the headmost position of the zoom lens assembly, a second group of lenses (11) which is placed next to the first group of lenses (10), a second lens barrel (13) in which the second group of lenses (11) is assembled, a first threaded bearing (12) formed as a part of the second lens barrel (13) of the second group of lenses (11), a first position stabilizing fork (14) which is formed on one side of the second lens barrel (13) of the second group of lenses (11) opposite to the first threaded bearing (12), a first stepping motor (15) with a first male screw rod (16) provided as an extension of the motor shaft, which is screwed into the bearing hole of the first threaded bearing (12) of the second group of lenses (11) and engages with the thread provided on the inner wall of the bearing hole of the first threaded bearing (12), a third group of lenses (17) which is placed next to the second group of lenses (11), a third lens barrel (19) in which the third group of lenses (17) is assembled, a second threaded bearing (18) formed as a part of the third lens barrel (19) of the third group of lenses (17), a second position stabilizing fork (20), which is formed on one side of the third lens barrel (19) of the third group of lenses (17) opposite to the second threaded bearing (18), and a second stepping motor (21) with a second screw rod (22) provided as an extension of the motor shaft, which is screwed into the bearing hole of the second threaded bearing (18) of the third group of lenses (17) and engages with the thread provided on the inner wall of the bearing hole of the second threaded bearing (18). All these component parts are assembled on an assembly base (23) on which an image sensor (24) like CCD or C-MOS is placed just underneath of the rearmost element of the lens assembly.
The instant that the power zooming switch of either telephoto or wide angle is turned on, the stepping motors (15 & 21) start moving simultaneously and the two groups of lenses (11 & 17) start moving to control zooming of the total lens in the telephoto direction or wide-angle direction receiving the zooming position signals of the zoom lens, which are programmed beforehand and written in the MCU of the DSC as the lens moving data to control each group of lenses for each focal length position.
Though the so far mentioned zooming control system could eliminate the conventional grooved cams which are expensive and difficult to make, it has still a shortcoming that due to the extended male screw shafts of stepping motors the total length or size of the zoom lens module becomes inevitably and relatively long.
The inventor of the subject application further develops a new mechanism of zoom lens module for DSCs that_can shorten the length of the zoom lens module and minimize the total size of DSC itself and will be described in detail hereinafter.